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Page 6 of 9 Valiev. Microstructures 2023;3:2023004 https://dx.doi.org/10.20517/microstructures.2022.25

Table 1. Structural parameters of CP Ti Grade 4 after various processing regimes
Average grain size, Total dislocation Size of second-phase Volume fraction of second-phase
State -2
d, µm density, ρ, m particles, r, nm particles, f, %
14 3
Hot rolled 10.00 ± 2.00 ≈ 2.4*10 10 2-3
15
HPT 0.12 ± 0.03 ≈ 2.1*10 - < 1
HPT + 700 5.00 ± 1.00 ≈ 2.2*10 14 35 ± 7 4-5
15
HPT + 700 + HPT 0.09 ± 0.03 ≈ 1.6*10 - < 1
14
HPT + 700 + HPT 0.12 ± 0.04 ≈ 2.3*10 18 ± 10 7-8
+ 350

Table 2. Mechanical properties of Ti Grade 4 in various structural states
State Microhardness, HV σ , MPa σ , MPa ε, %
B
0.2
Hot rolled 237 ± 2 500 680 23.9 ± 1.4
HPT 353 ± 7 1020 1170 8.9 ± 1.2
HPT + 700 266 ± 5 600 720 30.8 ± 2.0
HPT + 700 + HPT 423 ± 8 1200 1340 0.9 ± 0.4
HPT + 700 + HPT + 350 433 ± 3 1340 1510 9.5 ± 2.0

σ : Yield stress; σ : tensile strength; ε: elongation to failure.
0.2 B
Table 3. Calculated contributions of various strengthening mechanisms to the strength of UFG Ti Grade 4 and experimental data on
yield strength values for all analyzed states
State σ , MPa σ T calc , MPa σ , MPa σ , MPa σ , MPa σ , MPa σ , MPa σ , MPa
gb
0
T
dis
SL
Or
ss
Hot rolled 500 480 80 140 150 110 0 0
HPT 1020 980 350 440 0 0
HPT+700 600 600 200 140 70 0
HPT + 700 + HPT 1200 1170 400 380 0 200
HPT + 700 + HPT + 350 1340 830 340 150 150 0
boundary segregations during the formation of UFG structures in metallic materials using SPD techniques.
However, their nature and morphology are closely related to the processing regimes.

CONCLUSION
Recent studies show that the strength of UFG materials processed by SPD techniques is traditionally much
higher than that predicted by the Hall-Petch relation. The physical nature of this phenomenon is related to
the fact that the strength properties of UFG materials result not only from the presence of ultrafine grains
but also from other nanostructural features, including the formation of subgrain dislocation structures,
nanotwins, nanosized second-phase precipitations and the grain boundary structure, their non-equilibrium
nature and the presence of grain boundary segregations of impurities or alloying elements. The latter factor
is very important since it may contribute significantly to the strength of UFG materials. Moreover, the
segregations at grain boundaries can also affect the ductility of such metals and alloys. In particular, as has
recently been shown, the presence of grain boundary Zn in Al alloys with ultrafine grains leads to the
phenomenon of superplasticity at lower temperatures . In this regard, the nature of grain boundary
[27]
segregations and their behavior in deformation mechanisms is a relevant and exciting problem. The coming
years may witness the study of strengthening mechanisms and their control using SPD techniques to
become a relevant trend in the development of metallic materials with not only very high strength but also
ductility and other enhanced mechanical properties.